Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $149.72   13.164%   $169.4291   $169.43   $169.45   $169.40  
  Purchase #2 $11.25   8.472%   $12.2031   $12.20   $12.20   $12.20  
  Purchase #3 $36.99   11.816%   $41.3607   $41.36   $41.35   $41.40  
  Purchase #4 $69.35   7.604%   $74.6234   $74.62   $74.60   $74.60  
  Purchase #5 $20.36   6.725%   $21.7292   $21.73   $21.75   $21.70  
  Purchase #6 $100.99   10.154%   $111.2445   $111.24   $111.25   $111.20  
  Purchase #7 $99.87   10.500%   $110.3564   $110.36   $110.35   $110.40  
  7 purchase totals = $488.53       $540.9464   $540.94   $540.95   $540.90